Stereospecific Synthesis and Photophysical Properties of Propeller-Shaped C90H48 PAH

Highly twisted large PAHs offer, in addition to physical properties, a feature of chirality, which results in non-super imposable mirror-image structures of these compounds that can be resolved into optically active enantiomers. This process, however, is cumbersome, which largely restricts the available quantity of materials in optically active form and represents a great hurdle for their applications. Herein, we have synthesized an enantiomerically pure propeller-shaped PAH, C90H48, possessing three [7]helicene and three [5]helicene subunits. This compound can be obtained in gram quantities in a straight-forward manner. The photophysical and chiroptical properties were investigated using UV−vis absorption and emission, optical rotation and circular dichroism spectroscopy, supported by DFT calculations. The non-linear optical properties were investigated by two-photon absorption measurements using linearly and circularly polarized light. The extremely twisted structure and packing of the homochiral compound were investigated by single crystal X-ray diffraction analysis